linux-kernel - Re: [PATCH rfc v2 01/10] mm: add a generic VMA lock-based page fault handler

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Message-ID: <26989657-3ad9-48c5-9863-12993b78141c@huawei.com>
Date:   Sat, 26 Aug 2023 08:56:28 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <surenb@...gle.com>, <willy@...radead.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <loongarch@...ts.linux.dev>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-riscv@...ts.infradead.org>,
        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH rfc v2 01/10] mm: add a generic VMA lock-based page fault
 handler



On 2023/8/24 15:12, Alexander Gordeev wrote:
> On Mon, Aug 21, 2023 at 08:30:47PM +0800, Kefeng Wang wrote:
> 
> Hi Kefeng,
> 
>> The ARCH_SUPPORTS_PER_VMA_LOCK are enabled by more and more architectures,
>> eg, x86, arm64, powerpc and s390, and riscv, those implementation are very
>> similar which results in some duplicated codes, let's add a generic VMA
>> lock-based page fault handler try_to_vma_locked_page_fault() to eliminate
>> them, and which also make us easy to support this on new architectures.
>>
>> Since different architectures use different way to check vma whether is
>> accessable or not, the struct pt_regs, page fault error code and vma flags
>> are added into struct vm_fault, then, the architecture's page fault code
>> could re-use struct vm_fault to record and check vma accessable by each
>> own implementation.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>> ---
...
>> +
>> +vm_fault_t try_vma_locked_page_fault(struct vm_fault *vmf)
>> +{
>> +	vm_fault_t fault = VM_FAULT_NONE;
>> +	struct vm_area_struct *vma;
>> +
>> +	if (!(vmf->flags & FAULT_FLAG_USER))
>> +		return fault;
>> +
>> +	vma = lock_vma_under_rcu(current->mm, vmf->real_address);
>> +	if (!vma)
>> +		return fault;
>> +
>> +	if (arch_vma_access_error(vma, vmf)) {
>> +		vma_end_read(vma);
>> +		return fault;
>> +	}
>> +
>> +	fault = handle_mm_fault(vma, vmf->real_address,
>> +				vmf->flags | FAULT_FLAG_VMA_LOCK, vmf->regs);
>> +
>> +	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
>> +		vma_end_read(vma);
> 
> Could you please explain how vma_end_read() call could be conditional?

The check is added for swap and userfault, see

https://lkml.kernel.org/r/20230630211957.1341547-4-surenb@google.com
> 
>> +
>> +	if (fault & VM_FAULT_RETRY)
>> +		count_vm_vma_lock_event(VMA_LOCK_RETRY);
>> +	else
>> +		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
>> +
>> +	return fault;
>> +}
>> +
>>   #endif /* CONFIG_PER_VMA_LOCK */
>>   
>>   #ifndef __PAGETABLE_P4D_FOLDED